5,728 research outputs found
Diffusion of fluorine adatoms on doped graphene
We calculate the diffusion barrier of fluorine adatoms on doped graphene in
the diluted limit using Density Functional Theory. We found that the barrier
strongly depends on the magnitude and character of the graphene's
doping (): it increases for hole doping () and decreases
for electron doping (). Near the neutrality point the functional
dependence can be approximately by where
meVcm. This effect leads to significant
changes of the diffusion constant with doping even at room temperature and
could also affect the low temperature diffusion dynamics due to the presence of
substrate induced charge puddles. In addition, this might open up the
possibility to engineer the F dynamics on graphene by using local gates.Comment: 4 pages, 4 figure
Constraining the parameters of globular cluster NGC 1904 from its variable star population
We present the analysis of 11 nights of V and I time-series observations of
the globular cluster NGC 1904 (M 79). Using this we searched for variable stars
in this cluster and attempted to refine the periods of known variables, making
use of a time baseline spanning almost 8 years. We use our data to derive the
metallicity and distance of NGC 1904. We used difference imaging to reduce our
data to obtain high-precision light curves of variable stars. We then estimated
the cluster parameters by performing a Fourier decomposition of the light
curves of RR Lyrae stars for which a good period estimate was possible. We also
derive an estimate for the age of the cluster by fitting theoretical isochrones
to our colour-magnitude diagram (CMD). Out of 13 stars previously classified as
variables, we confirm that 10 are bona fide variables. We cannot detect
variability in one other within the precision of our data, while there are two
which are saturated in our data frames, but we do not find sufficient evidence
in the literature to confirm their variability. We also detect a new RR Lyrae
variable, giving a total number of confirmed variable stars in NGC 1904 of 11.
Using the Fourier parameters, we find a cluster metallicity [Fe/H]_ZW=-1.63 +-
0.14, or [Fe/H]_UVES=-1.57 \pm 0.18, and a distance of 13.3 +- 0.4 kpc (using
RR0 variables) or 12.9 kpc (using the one RR1 variable in our sample for which
Fourier decomposition was possible).Comment: 14 pages, 11 figures, accepted for publication in A&
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